1. Field of the Invention
This invention relates generally to a digital disc playback apparatus of the kind having a digital disc on which two-channel digital audio signals are recorded and, more particularly, to a disc playback apparatus in which digital data other than the audio signals are recorded thereon and are utilized upon playback.
2. Description of the Prior Art
A system employing an optically encoded digital audio disc, which has become known as a compact audio disc or a digital audio disc, is known to reproduce high quality stereophonic musical signals. In such systems, the audio data is recorded generally as pits in the surface of the record, and the data is read out by a laser device in the playback system. Presently, only audio information has been encoded on such discs, however, it is contemplated that data representing characters, display data, program data, or data other than conventional stereophonic audio signals could also be reproduced by such optical digital audio disc system. Moreover, it would appear that it would be advantageous if such data other than audio information could be reproduced without extensive modifications to the present disc playback system. For example, it would be beneficial if it were possible to realize playback apparatus to reproduce visual information, such as charts, statistics, and graphs, as well as pictorial illustrations such as still pictures or video games simply by adding a suitable visual display unit to the playback apparatus. In this fashion, the compact disc system would provide a wide range of applications beyond the present audio applications.
These uses other than audio might also be obtained by using flexible magnetic discs, known as "floppy discs", however, the memory capacity of such discs is not large. The data memory capacity currently available in compact audio disc is around 500 megabytes, and this capacity is much greater than the memory capacity of a standard flexible memory disc, thereby providing great advantages to a system employing a compact audio disc as the memory.
On the other hand, because the compact discs have been principally developed and utilized solely for the reproduction of audio signals, the capability of searching on the disc for relative large informational units, such as musical programs, is coarse. That is, the beginning of the data on the disc is searched on a relatively large basis for large information units, such as music program segments. This is in conflict with the requirements relative to other uses, which must be read out and identified on a much smaller unit basis, for example, on the order of 128 bytes to ten kilobytes. This presents a distinct problem in attempting to use the compact disc for purposes other than recordation of stereophonic audio signals.